Steam generator



March 7, 1961 Filed July 27. 1953 W. H. ARMACOST STEAM GENERATOR 2sheets sheet 1 Fan Speed Regulator Recirculation Air Preheuter'INVENTOR.

Wilbur H. Armucos'r ATTORNEY W. H. ARMACOST March 7, 1961 STEAMGENERATOR 2 Sheets-Sheet 2 Filed July 27. 1953 Burning Fuel Mlxiure on ao o 0 0 Fig. 2.

Burning FueI Mixture y Recirculoted Gas Recirculuted Gas Fig. 5.

IN VEN TOR.

Wilbur H. Armucosi A TTORNE Y ,Um'wd Stat-s8 Paren 1,913,750 STEAMGENERATOR Wilbur H.,Armacost, Scarsdale, N.Y., assignor to CombustionEngineering, Inc., New York, NY a corporation of Delaware Filed July'27,1953, Ser. No. 370,487

" "12 Claims. 01. 122- 479 cooled furnaces is disclosed in KreisingerPatent 2,363,

875, dated November 28, 1944, and involves tilting the burners upwardlyor downwardly from a horizontal firing plane so as to thus locate thezone of intense combustion nearer to or farther from the furnace outletin order to vary the amount of heat absorbed byradiation to the furnacewalls, and thereby to increase or decrease,

respectively, the temperature of the. gases exiting from the furnace tosubsequently flow over the elements of the convection steam heater. Inanother method fixed burners are disposed at the corners of the furnaceand project the jets of fuel and air in directions tangential 2,973,750Patented Mar. 7, 196i increased so that a desired steam temperature maybe the quantity of gas recirculated. p

7 An object of this invention is to provide an improved steam generatingand superheating installation in which the final steam temperature maybe controlled by varying the weight of gases from the furnace chamberflowing overthe steam superheater elements in addition to the controlobtained by the effect of varying either the horizontal or. verticalangle of firing by the burners as mentioned above. g

It is a further object of the invention to provide an improved steamgenerating and superheating installation of the kind inwhich gases ofcombustion returned to the furnace for recirculation through theinstallation with fresh gases will be so distributed in the furnace withrespect to the mass of burning fuel and gases therein as to permiteither increase or decrease in the superheating efiect of the gasespassing from the furnace.

According to the present invention, in order to obtain the requiredfinal steam temperature, and to control such temperature, the steamgenerating and superheating installation comprises means for controllingthe amount of heat abstracted from the fresh products of combustionwithin the furnace both by altering the combustion zone before suchproducts reach the superheating surface, and means for increasing theweight of gas flowing from the furnace chamber over said superheatingsurface by returning to the furnace and recirculating through theinstallation, with the fresh products of combustion, a regulatedquantity of gases of combustion which has already passed through theinstallation or a part thereof.

Further, according to this invention there may be interposed at someconvenient location in the path of the gases recirculated through thefurnace a fan or other device effective to increase or reduce thevelocity of the gases to a point above or below the velocity of fuel andto an imaginary circle whose center is the vertical axis of. the furnaceas in the Kruger Patent No. 2,243,909, dated June 3, 1941. The burnersare arranged to be swung in a horizontal plane for varying the SIZE, ofthe circle and hence the distance of the zone of intense coin I greef'ofcontrol obtainableby. burnenposition adjustment only. 7 a

V ithla convectively heated superheater a given quantity of steam can beraised to the required temperature by flowing over the superheatingsurface either a predetermined weight of gases at a sufficiently hightemperature or a greater weight of gases at a lower temperature.Recirculation of gases which have flowed over the superheating and otherheat absorbing surface of the installation constitutes another method ofreducing the quantity of heat absorbed by the furnace wall cooling andsteam generating tubes as disclosed in De Baufre Patent 2,229,643, datedJanuary 28, 1941. In

this method gases which have passed through the installation are causedto enter the furnace chamber and i with the fresh combustion products.The absorption of heat by radiationto the furnace walls is reduced andthe mass of gas flowing over the superheater is also air entering thefurnace so as to increase or decrease turbulence set up within thefurnace and therebyvary the temperature of the gases discharged from thefurnace to passover the steam heater.

The gases returned to-the furnace may be discharged thereinto throughnozzles appropriately disposed in relation to the level of location ofthe burners by which the furnace is fired, and where the burners arearranged to tilt, the returned gas nozzles may also be arranged to tiltbut preferably independently thereof.

The accompanying drawings diagrammatically illustrate steam generatorsembodying the features of the present invention for superheated steamtemperature control. v

Figure 1 is a diagrammatic elevational view of a steam generatorembodying gasreciriculation to the furnace for superheat regulation inaccordance with the present in :vention.

Figures 2 and 3 are views along the lines 2-2 and 3-3,

respectively, in Figure 1 illustrating different relations within thefurnace of the mass of burning fuel and the volume of recirculatedgases.

Figure 4 is a view similar to Figure 1 but illustrating a differentarrangement of the fuel burners of the furnace with respect to the gasrecirculation nozzles; and

Figure 5 illustrates an additional arrangement of the fuel burners withrespect to the gas nozzles.

According to the embodiment of the invention illustrated in Figure l thefurnace 10 is assumed to be fired by four sets 11, 12, 13, 14 of burners15 disposed at the corners of the furnace, i.e. in or closely adjacentthe angles formed at the junctions of the vertical walls. Other nozzles16 discharging gases into the furnace, for recirculation through theinstallation also may be located at the corners of the furnace in twosets at 17, 18 conefiiciency for combustion.

Any suitable means may be provided for varying independently theinclination of the fuel burners 15. in the vertical or horizontal planeand for independently varying the. inclination to the horizontal of thereturngas nozzles 16in order to regulate the temperature of the gasesleaving the furnace and flowing over the superheater.

In Operation when all of the burners are adjusted to project the fueland air streams in substantially horizontal directions tangent to theimaginary vertical cylinderlocated centrally of the furnace 10, theburning fuel streams issuing from the four sets 11,12, 13, 1 4 of thecorner located burners 15 impinge upon one another resulting in aturbulent, rotating mixture with a consequent rapid rate of combustion.This rapid combustion produces a very high temperature in a zone A atthe level of the burners near the bottom of the furnace so that there isa high rate of heat transfer from the flames to the water cooled wallsin this zone both by radiation and by convection. Leaving this zone thehot products of combustion pass upwardly and continue giving off heat tothe water cooled walls thereabove and exit from the furnace cooled to arelatively low temperature. When all of the burners 15 are directedupwardly, the streams of fuel are still tangent to an imaginary verticalcylinder in the furnace but the impingement of the burning fuel streamsupon one another is much less than when the burners are horizontallydirected as above described. This results in but relatively littlemixing and turbulence and; consequent slower or delayed combustion. Thisdelayed combustion occurs in a zone B, that is located higher in thefurnace than the zone A, and extends well into the upper part of thefurnace. Consequently the temperature of the products of combustionleaving the furnace is relatively high because of the shorter paththrough which they pass from the combustion zone to the outlet of thefurnace 1t} and because the heat transfer from the flames to the Watercooled walls 20 at the bottom of the furnace is substantially less thanwith horizontally directed streams. The change in direction of thefuelstreams from the horizontal to an upward inclination results in arise in the temperature of the gases leaving the furnace which has beenfound adequate to change the rate of heat absorption by the superheater22 so that the steam temperature may be raised to that required forsatisfactory operation over a considerable range of ratings of the steamgenerating unit.

The gases after flowing over the superheater 22, or the supcrheaters anda reheater.23. if included in the unit, usually pass over an economizer24 and other heat exchangers such as an air preheater 26. After flowingthrough the latter they. are deliveredby the induced draft fan towardsthe chimney or stack through duct 32. An additional fan 34 is providedaccording to this invention and located are suitable point in' relationto the fan 22 in a conduit 36 leading back to the gas nozzles 16 from asuitable point downstream of the superheater 22. Dampers 37, 38 areprovided on both ducts for regulating the volume of gas flowing throughthe' nozzles 16 supplied by conduit 36 into the furnace 10, dampers 37being associated with the upper nozzle sets 17 and dampers 38 with lowernozzle sets 18. Thus, a portion of the gases of combustion is deliveredby the fan 30 for recirculation and as determined by the setting of thedampers 37, 33 flows from conduit 36 through branch ducts to the gasnozzles 16. i

By tilting the gas nozzles 16 in unison with the fuel burners 15 thegases may be introduced in streams generally parallel with the air andfuel streams delivered by the burners, and a greater uniformity of gasdistribution than heretofore is obtained without detriment to the Whenthe lower set 18 of gas nozzles 16 is used alone,

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the recirculated gas is forced to the center of the furnace 1 0due tothe fuel and air coming in from burner sets 11, 12, 13, 14 thereabove,the burning fuel and air mixture having a tendency to stay closer to thewalls 20 as illustrated in Figure 2. Consequently, with this method of'firing more heat is absorbed in walls 20; particularly radiant, and thegas temperature leaving the furnace 10 is lower than without gasrecirculation. When the upper row 17 of recirculating tilting nozzles isused, the gas therefrom would hug the furnace walls while the fuel firedtangentially below is forced out into the center of the furnace 10 asshown in Figure 3. Thus, less radiant heat would be given to walls 20 sothat the gas temperature would be higher leaving the furnace than ifthere were no recirculation of gases.

Another variation of control may be obtained by regulating the speed offan 34 to vary the velocity of the recirculated gas entering the furnaceso that it is either above or below the velocity of the air and fuelentering the furnace through burners 15; changing the ratio of thesevelocities increases or decreases the turbulence set up in the furnace.

By using tilting nozzles for gas recirculation, a variation on theseconditions is obtained due to increasing or decreasing the area offurnace walls 20 scrubbed by the gas recirculated coupled with the usualeffect attained by tilting of the fuel and air streams, the tilting ofthe gas nozzles being independent of the tilting of the fuel burningequipment.

Furtherfby using tilting nozzles for the introduction of recirculatedgases a much wider control may be obtained than by using fixed nozzles.If one row 17 of tilting recirculation nozzles is applied between rows12 and 1 3 of bur ner s as Figure 4, results are attained at a low loadorja high load: that are equivalent to those accom lished by. using thetwo individual rows 17, 18 as in Figure 1, since at low load, either thetop two rows 11, 12 of burners or the two bottom rows 13, 14 of burnersmay be utilized to obtain the desired effect of gas recirculation on themasses of fuel and air.

Ttilting recirculation gas nozzles may also be applied in the cornersofthe furnace, that is, fired with horizontal fixed burners in thewalls, as. indicated in Figure 5 insteadof tangential burners whetherfixed or tilting.

It will be appreciated that by varying the angle to the horizontal ofthe burners 15, and also by manipulation of the hereinabove mentioneddampers 37, 38, an efficient regulation can be effected of thetemperature as well as the quantity of gases flowing over thesuperheater, and thus the steam temperature may be controlled.

' What I claim, is:

l. The. method of regulating temperature of steam from a heaterabsorbing its heat mainly by convection from gases leaving a water tubecooled furnace comprising; introducing fuel and air into the furnace forcreating a gas mass to radiate heat to the water tubes iithereoffmaintaining, for a given load, a substantially uniform rate" of fuelfiring; passing the gases from the furnace over the steam heater forheating steam passing therethrough; adjusting the firing angles of thefuel burners for regulating. the temperature of gases passing over thesteam heater by changing the, position of the zone of combustionwithrespect to portions of the water cooled furnace walls; and as the steamtemperature varies reintroducing into the furnace a volume of gases thathas already been passed. over the superheater, the volume ofrecirculated gases being introduced between said gas mass in the zone ofcombustion and said tubes when the supernace for 'creating'agas mass toradiate heat to the water tubes thereof; maintaining, for a given load asubstantially uniform rate of fuel firing; passing the gases from thefurnace over the steam heater for heating stea'mpassing there through;adjusting thefiring angles of the fuel heater absorbing its heat mainlyby convection from gases leaving the outlet of a water tube cooledfurnace comprising; introducing fuel and air into the furnace forcreating a gas mass to radiate heat to the water tubes thereof;maintaining, for a given load, a substantially uniform rate of fuelfiring; passing the gases from the furnace over the steam heater forheating steam passing therethrough; adjusting the firing angles of thefuel burners for regulating the temperature of gases passing over the,steam heater by lowering or raising the position of the zoneofcombustion with respect to the outlet of the water cooled furnace assteam temperature rises or falls, respectively; and as the steamtemperature varies reintroducing into the furnace a volume of gases thathas already been passed over the superheater, the volume of recirculatedgases being introduced above said zone of combustion when the superheattemperature falls and 7 below said zone of combustion to when thesuperheat through a passage containing heat absorbing apparatus andwherein'fuel and air is introduced into the furnace in directionstangential to an imaginary horizontal circle 7 in the furnace forcreating a turbulent massof burning fuel and-products of combustioninsaid furnace at a level above the bottom thereof; which methodcomprises:

the steps of increasing or decreasing the absorption of 74 heat in saidfurnace wall tubes by diverting products of combustion ..at a pointbeyond said heat absorbing apparatus infthe direction of gasflow andintroducing the 'recirculatedgas into said furnace from a point; belowthe pointof fuel'introduction and in an upward direction 2' toward thefuel mass in the center of the furnace so as-ito displace the mass ofgas and products of combustion laterally from the center of the" furnacetoward said furnace wall'tubesto'increase the absorption or heat in saidfurnace wall tubes and from a point above the point of fuel introductionand in an upward direction between the fuel mass and the furnace walltubes to decrease the heat absorption in said tubes.

5. A method of varying heat absorption in a furnace having 'fluidcirculation tubes on its walls and from which the products of combustionflow through a passage containing heat absorbing apparatus and whereinfuel and air is introduced into the furnace in directions tangential toan imaginary horizontal circle in the furnace for creating a turbulentmass of burning fuel and products of combustion in said furnace at alevel above the bottom thereof and gaseous products of combustion arediverted away from a point beyond said heat absorbing apparatus in thedirection of gas flow, which method comprises the steps of: decreasingthe absorption of heatin the furnace walls by introducing therecirculated gas into said furnace from a point above the point of fuelintroduction and directing the recirculated gas upwardly adjacent thefurnace walls so as to form a layer of recirculated gas surrounding thefuel mass so as to displace the mass of gas andproducts ofcombustionlaterally away fromsaid furnace wall tubes; and increasing theabsorption of heat inithe furnace walls by introducing the recirculatedgas a from below said point of fuel introduction and in an upwarddirection into the center of the burning fuel and gas mass fordisplacing the latter outwardly toward said wall tubes. A r

6. A method of varying heat absorption in a furnace having fluidcirculation tubes on its walls and from which the, products ofcombustion flow through a passage containing heat absorbing apparatusand wherein fuel'and air is introduced into the furnace in directionstangential ,to an imaginary horizontal circle in the furnace forcreating a turbulent massof burning fuel and products of combustion insaid furnace at a level above the bottom thereof and gaseous productsofcombustion are diverted from a point beyond said heat absorbingapparatus in the'direction of gas flow, which method comprises the stepsof: decreasing the absorption of heat in the furnace walls byintroducing the recirculated gaseous products of combustion into saidfurnace in directions tangential to said imaginary circle from a pointabove the point of fuel introduction and directing the recirculatedproducts of combustion so as to form a layer of recirculatedgassurroundingthe fuel massso as to displace the mass of gas andproducts of combustion laterally away from said furnace wall'tubes; andincreasing the absorption of heat in the furnace walls by introducingthe recirculated" gaseous products of combustion from below said pointof fuel introduction and in an upward direction into the center-of theburning fuel and gas mass for displacing the latter outwardly towardsaid wall tubes.

7. A method of varying heat absorption in an elongated verticalfurnacehaving fluid circulation tubes on its walls and from which the productsof combustion .flow through a passage containing heat absorbingapparatus and wherein fuel and air is introduced into the furnace indirections tangential to an imaginary horizontal circle in the furnacefor creating a turbulent mass of burningfuel and products of combustionin said furnace at a level-above the bottom thereof; which methodcomprises the steps of: decreasing the amount of absorption of heat insaid furnace wall tubes by diverting gaseous products of combustion thathave passed over said heat exchanger from said outlet and introducingthe recirculated gases into said furnace at a point upstream ofrthepoint of fuel introduction in the sense of gas flow; and directing therecirculated gas to flow outwardly of the mass of burning fuel and gasmass between it and said furnace wall-tubes so as to shift'the burningfuel and gas mass inwardly toward the center of said furnace away fromsaidfurnacewall tubes. 7

8. The method of regulating temperature of steam from a heater absorbingits heat mainly by convection from gases leaving the outlet of a Watertube cooled furnace comprising; introducing fuel and air into thefurnace for creating a gas mass to radiate heat to the water tubesthereof; maintaining, for a given load a substantially uniform rate offuel firing; passing the gasesfrom the furnace over the steam heater forheating steam passing therethrough; and as the steam temperature falls,raising the temperature of gases passing over the steam heater byadjusting the firing angles of the fuel burners to move the zone ofcombustion closer to the furnace outlet while reintroducing into thefurnace a volume of gases, that has already been passed over thesuperheater and other heat exchange surface, at a point above said zoneof combustion and in a direction to flow adjacent the wall tubes.

9. In a steam generator having an elongated vertical furnace with fluidcirculation tubes on its walls and from the outlet of which the productsofcombustion flow to an offtake duct through a passage containing asteam heater; a set of burners so mounted in said 7 walls as tointroduce fuel'and air into the furnace in directions tangential to animaginary horizontal cylinder in said furnace at a level above thebottom thereof; a conduit for diverting products of combustion away fromsaid oiftake connecting with said passage at a point beyond said steamheater in the direction of gas flow; sets of tangentially mountednozzles located in the furnace walls above and below said set of burnersand connected to receive products of combustion from said conduit andintroduce them into said furnace so as tovary the amount of heatabsorbed in said furnace through radiation to said furnace wall tubes;means associated with the upper set of gas nozzles operable to directthe streams of gas therefrom along the furnace walls above the burningmass'of fuel and between said mass and the furnace walls to decrease theradiant absorption of heat thereby; means associated with the lower setof gas nozzles operable to direct the streams of gas therefrom upwardlyinto the mass of burning fuel thereabove for displacing the said massoutwardly toward the furnace walls for increasing theradiant absorptionof heat thereby.

10. In a steam generator having an elongated vertical furnace with fluidcirculation tubes on its walls and from the outlet of which the productsof combustion flow to an olftake duct through a passage containing asteam heater; a set ofburners so mounted in said walls as to introducefuel and air into the furnace in directions tangential to an imaginaryhorizontal circle in said furnace at a level above the bottom thereof; aconduit for diverting products of combustion away from said offtakeconnecting with said passage at a point beyond said steam heater in thedirection of gas flow; sets of tangentially mounted nozzles located inthe furnace walls above and below said set of burners and connected toreceive products of combustion from said conduit and introduce them intosaid furnace so as to vary the amount of heat absorbed in said furnacethrough radiation to said furnace wall tubes; and means associated withthe upper set of gas nozzles operable to direct the stream of gastherefrom along the furnace walls above the burning mass of fuel andbetween said mass and the furnace walls to decrease the radiantabsorption of heat thereby.

11. In a steam generator having an elongated vertical furnace with fluidcirculation tubes on its walls and from the outlet of which the productsof combustion fiow to an oiftake duct through a passage containing asteam heater; a set of burners so mounted in said walls as to introducefuel and air into the furnace in directions tangential to an imaginaryhorizontal circle in said furnace at a level above the bottom thereof; aconduit for diverting products of combustion away from said offtakeconnecting with said passage at a point beyond said steam heater in thedirection 'of gas flow;

sets of tangentially mounted nozzles located in the furnace walls aboveand below said set of burners and connected to receive products ofcombustion from said conduit and introduce them into said furnace so asto vary the amount of heat absorbed in said furnace through radiation tosaid furnace wall tubes; means associated with the lower set of gasnozzles operable to direct the streams of gas therefrom upwardly intothe mass of burning fuel thereabove for displacing the said massoutwardly toward the furnace walls for increasing the radiant absorptionof heat thereby.

12. In a steam generator having an elongated vertical furnace with steamgenerating tubes on its walls and from which the products of combustionflow through a passage containing heat absorbing apparatus, a set oftiltable burners so mounted in said walls as to introduce fuel and airinto the furnace in directions tangential to an imaginary horizontalcylinder in the furnace for creating a turbulent mass of burning fueland products of combustion in the furnace; a gas recirculation conduitconnecting with said gas passage at a point downstream beyond said heatabsorbing apparatus; gas nozzles tiltable about their horizontal axeslocated in the furnace walls 'above and below said set of burners andconnected to receive products of combustion from said conduit so as tointroduce streams of recirculated gas into said furnace at levels aboveand below said set of burners; the method or operating said steamgenerator which comprises; tilting said set of burners about theirhorizontal axes for raising or lowering the zone of combustion in thefurnace to thereby decrease or increase the radiant absorption of heatby said wall tubes; and tilting said gas nozzles about their horizontalaxes independently of tilting of said burner sets for directing streamsof recirculated gas into the center of the burning mass of fuel andproducts of combustion from the lower set of nozzles and for directingsaid streams of recirculated gases between said burning mass of fuel andthe, furnace wall tubes when the upper set of burners is in operation soas to respectively increase or decrease the amount of radiant absorptionof heat by said furnace wall tubes.

References Cited in the file of this patent UNITED STATES PATENTS1,791,955 Cannon Feb. 10, 1931 2,013,565 Lundgren Sept. 3, 19352,363,875 Kreisinger et a1. Nov. 28, 1944 2,685,279 Caracristi Aug. 3,1954 2,781,746 Armacost et a1 Feb. 19, 1957 FOREIGN PATENTS 827,384Germany Ian. 10, 1952 504,114 Great Britain Apr. 14, 1939

